The key to understanding the leaven of the Pharisees (Matthew 16:6, 11-12) does not hinge on their zeal in keeping the law, but on their zeal in finding loopholes to twist it to their own ends. Their motto could have been, "How close can we get to the edge without going over?" We could refer to this practice as brinkmanship (pushing a situation to the limit to force a desired result) or marginalism (taking an extreme position on an issue).
A former homiletics teacher, also an avid skier, conveyed to his class an analogy of the Ten Commandments as the boundary markers along the ski trail. Every year, when contemplating the boundary markers at Vail or Aspen, he reflected that only an idiot would ski as close to the edge as he could. Yet this describes many practices of the scribes and Pharisees!
The legalist and the lawbreaker both have a morbid curiosity about those boundaries rather than concentrate upon the vast latitude of choices between those markers. This is reminiscent of our parents Adam and Eve developing a morbid curiosity about the one tree that God forbade, ignoring the thousands upon thousands of varieties that He did not forbid (Genesis 2:16-17; 3:1-6). This behavior dwells on the negative and ignores the positive.
These examples point out that the spirits of legalism and lawlessness are twin siblings. When we place the critical points of the law/grace and legalism/lawlessness issue in proper perspective, law and grace are powerful allies opposing legalism and lawlessness. They give Christians great freedom to do good for others while also doing what is right.
David F. Maas
Righteousness from Inside-Out